This invention relates to a glass sealing type ceramic package, and more particularly to a glass sealing type ceramic package having a high density wire bonding enabling a high speed operation.
A conventional glass sealing type ceramic package is shown in FIG. 6, which includes a cavity b for storing a semiconductor device a, a ceramic substrate e having a first glass layer d on a first surface c, a ceramic cap h having a second glass layer g on a second surface f and a lead frame i. Lead frame i is supported and fixed by ceramic substrate e and ceramic cap h, opposing first and second surface c, f to each other. By fusing both first and second glass layers d, g and uniting them integrally, semiconductor device a is sealed hermetically in cavity b.
In connection with a high integration and high density of the semiconductor device, such glass sealing type ceramic package has a rectangular configuration. Usually, a so-called Cer Quad Package having lead frames in four directions is used widely. As shown in FIG. 6, the foregoing ceramic package has one stage lead frame electrically connected to semiconductor device a. In recent years, the number of gates is increased and a multipin or multi-lead frame is becoming more and more popular, so that the width of each lead frame is inevitably narrower and longer. As a result, the electrical properties such as wiring inductance .or conductivity resistance are deteriorated, thereby such ceramic package becomes unsuitable for use of a high speed semiconductor device.
When the semiconductor device is actuated at a high speed, the following problems take place: (1) A certain noise occurs in a ground and a power source. Since the value of noise is expressed with L (di/dt), dt becomes smaller and then the value of noise is greater, thereby causing malfunction. (2) When using such ceramic package in a higher frequency range, a signal transmission due to the inductance and capacitance of a signal pin is delayed.
To cope with the foregoing problems, the following ceramic package has been proposed in recent years. 1) A two-stage lead frame is supported and fixed by a glass layer as shown in FIG. 7. 2) In a ceramic package having a multilayer wiring structure, an internal wiring of one layer is a single power source wiring and connected to that of the other layer by way of a through hole or the like. Thus, the other lead frames can be used effectively for signal transmission. Refer to Japanese laid-open Patent Publication No. 1-111342. 3) By disposing a metallized layer on the bottom of the ceramic package, which will constitute a ground electric potential, the inductance and capacitance are kept constant. Refer to Japanese Laid-open Patent Publication 1-278760.
According to the foregoing conventional ceramic package, the lead frames, a wiring layer in a single power source and a metallized layer are placed one above another, thereby the ceramic package becomes complicated and its production cost becomes expensive.